Contemporary systems typically comprise a solenoid-operated purge valve that is under the control of a purge control signal generated by a microprocessor-based engine management system. A typical purge control signal is a duty-cycle modulated pulse waveform having a relatively low frequency, for example in the 5 Hz to 50 Hz range. The modulation ranges from 0% to 100%. The response of certain conventional solenoid-operated purge valves is sufficiently fast that the valve follows to some degree the pulsing waveform that is being applied to it, and this causes the purge flow to experience similar pulsations. Such pulsations may at times be detrimental to tailpipe emission control objectives since such pulsing vapor flow to the intake manifold may create objectionable hydrocarbon spikes in the engine exhaust. Changes in intake manifold vacuum that occur during normal operation of a vehicle may also act directly on the valve in a way that upsets the control strategy unless provisions are made to take their influence into account, such as by including a vacuum regulator valve. Moreover, low frequency pulsation may produce audible noise that may be deemed disturbing.
A general aspect of the present invention is to provide a canister purge valve that is capable of providing more accurate control in spite of influences that tend to impair control accuracy. In furtherance of this general objective, a more specific aspect is to provide a canister purge valve with a linear solenoid actuator. Other more specific aspects relate to various constructional features, such as details of the valve and seat elements.